Liquid cooled transmission line



Gd. 8, CROSBY 3,106,600

LIQUID COOL-ED TRANSMISSION LINE Filed June 15, 1960 INVENTOR. FIG. 2 23 HOWARD M. CROSBY f/Viw ATTORNEY nited States The present invention relates to a flexible, liquid-cooled radio frequency transmission line useful in conveying large amounts of radio frequency energy, as of the order of several hundred kilowatts, from a generator to a load.

The transmission line in accordance with my invention, comprises a plurality of spaced-apart thin wall copper tubes embedded in insulating material. The material and tubes are surrounded by a vinyl, or other suitable type of covering material, to form encased insulated thin wall flexible copper tubing. The opposite ends of the cable are gathered in a header member. The header is made hollow. High frequency power is conveyed onto the header. From the header surface material the power flows along the outer surface of the copper tubes. A coolant inlet is inserted into the hollow portion of the header member. Liquid-coolant flows through each of the tubes to the other end of the transmission line which terminates also in a header.

Prior art methods of transmitting high power radio frequency energy from the transmitter or generator to the load include rigid coaxial low impedance transmission lines consisting of a copper tube inner conductor surrounded by a large tubular outer conductor. However, flexibility is not obtained with such a line. Such devices are limited also in their power transmission capacity.

Another type of pror art flexible line consists of two flat thin copper strips separated by a suitable insulating or dielectric material. However, in such devices difficulty in cooling the strip occurs and heat resulting from losses in the conductor is not carried away. In one form of device, to overcome this diificulty, a strip line is provided. In this device channels are formed in the molded insulation of the cable to permit a liquid coolant to flow in partial contact with the copper strip to carry off the heat. This is not satisfactory for reasons of mechanical strength. Also, since the coolant is not in complete contact with the metal strip, heat must flow through the thin metal section to the points in contact with the coolant. The result is incomplete cooling, high heat spots and therefore necessary power derating of the cable. The outward pressure of the coolant against the relatively large flat surfaces tends to force the cable apart. In addition, lateral stresses tend to buckle the thin flat strip conductors. This device is flexible only in one direction. The wide strip prevents flexibility in the other direction.

The present invention overcomes these and other disadvantages of prior art radio frequency (RF) transmission lines. It provides complete and uniform cooling. No coolant pressure is exerted on the molded compound. In addition, the copper tubing is capable of withstanding relatively high pressures without rupture. A cable, constructed in accord with my invention, is more flexible in the lateral direction than prior art devices. It is flexible in a direction perpendicular to its width as well as in a direction perpendicular to its thickness. In one embodiment of the present device it is equally flexible in all directions.

Accordingly an object of the present invention is to provide a flexible liquid-cooled form of RF transmission line capable of conveying large amounts of radio frequency energy in the order of several hundred kilowatts from a generator to a load.

Another object of the present invention is to provide a flexible RF transmission line for conveying a high 3,1 0 6 ,(iilil Patented Oct. 8, 1963 radio frequency energy power load, and wherein are incorporated features of uniform, complete cooling and stronger mechanical configuration.

Another object of the present invention is to provide a flexible, but strong, RF transmission line capable of conveying large amounts of power, which is readily connectable to a generator and a load and to a source of coolant, which is uniformly and completely cooled and wherein coolant pressure is not exerted on the molded compound used as insulation.

Another object of the present invention is to provide a flexible, heat resistant, mechanically strong RF transmission line cable capable of conveying high power radio frequency energy, which line can stand relatively high coolant pressure without rupture.

While the novel and distinctive features of the invention are particularly pointed out in the appended claims, a more expository treatment of the invention, in principle and in detail, together with additional objects and advantages thereof is aflorded by the following description and accompanying drawing in which:

FIG. 1 is a pictorial representation illustrative of a. preferred embodiment of the inventive radio frequency (RF) transmission line.

FIG. 2 is a pictorial representation showing the separa-' tion of the header of FIG. 1 at the ends for connection to the two terminals of the RF circuit, and

FIG. 3 is a pictorial representation illustrative of another embodiment of the inventive RF transmission line.

Now referring to the drawings and particularly to FIG. 1, a plurality of thin walled copper tubes 12 may be arranged in two parallel rows, or banks 17 and 18, with each tube, optionally, either separated slightly from, or in direct contact with its neighbor. The entire assembly of copper tubes 12, which extends the length of the cable 13, is embedded in insulating material 14. Insulating material 14 may be composed of a low power loss silicone rubber compound. The silicone rubber compound is able to withstand high temperatures and at the same time provides electrical insulation. The silicone rubber used may be either GE type RTV-ZO, a silicone polymer, or Dow Corning X-350l4 silicone rubber compound, both of which will withstand high and low temperatures while retaining their good flexibility and electrical properties. Polyethylene and similar low-loss insulating materials could also be used if desired. This assembly is then covered with an abrasion resistant cover 10 of material such as rubber or vinyl covering of types well known in the art. Each sheet, or bank, of tubes, 17 and 18, enters into the back wall of and each tube is soldered to respective metal headers 15 and '16 at one set of terminal ends of the cable. The headers 15 and 16 form the electrical connections to the cable. There are four headers, two at each end and each of the headers at each end (for example headers 15 and 16) terminates one of the banks of copper tubes 17 or 18. The other ends of the tubes are terminated by headers '15 and 16' respectively as shown in FIG. 2. Each of the headers is hollowed as, for example, by preforming or by drilling or milling to permit liquid coolant to flow through the tubes. The tubes are joined together by the header and extend into the hollow portion of the header. A coolant inlet 19 is disposed perpendicularly to and enters the hollow portion of each of the headers 15 and 16. At the headers at the other end 15 and 16 coolant outlets 19' are provided.

The headers 15 and 16 are connected to a generator and the headers on the other end of the cable 13 are connected to the two inputs to the load. The radio frequency input energy introduced into headers 15 and 16 flows along the outer surfaces of the copper tubes 12.

The current flows approximately equally through the tubes if the physical dimensions, etc., of the copper tubes are substantially equal. The liquid coolant introduced through coolant inlets 19 flows through the interior of the hollow header or 16 to the entrance to the copper tubes .12. and therealong to the other tube ends. This provides complete and uniform cooling. No coolant pressure is exerted on the molded compound since flow is internal inside the copper tubes and the metal of the copper tubes withstands the force of the coolant flowing therethrough. The copper tubing because of its composition is capable of withstanding relatively high pressures without rupture and at the same time, the tubular shape, compared to prior art wide strips flexible in only one direction, aifords the advantage of improved flexibility in all directions and particularly in the direction at right angles to the width of the cable. The line is split approximately midway between the two banks of conductors 17 and 18 and this separation is at the terminal ends for a short distance back for soldering to the two headers which are connected to the two terminals of the RF input circuit. Similar separation is made between the tube banks at the other cable end for connection of each of the two headers at that end to one of the two terminals of the load circuit.

In use the upper and lower portions of the cable tube rows 17 and 18 are similar to a two wire connection. The upper header 15 may be connected, for example, to the high voltage side of the generator and its opposite end header 15 connected to the high side of the load. The header 16 then is connected to the low side of the load and the header 16 is connected to the low side of the generator. Headers 15 and .16 are separated by the insulation between the high and low portions of the generator. Headers 15 and 16' are similarly separated at the load. The inner and outer headers of the cable of FIG. 3, to be described, are similarly separated.

The spigots '19 may be connected to separate hoses of rubber, vinyl or other electrical insulating material. The hoses are of length such that substantially complete attenuation of voltage in the high electrical resistance water or other coolant occurs along the length of flow. At the other end of the hoses the supply pipe may be split into a Y and each rubber hose connected to one branch. At the other end of the cable 10, tubes 19 are connected similarly to separate rubber hoses which are also of length for attenuation of voltage along the coolant emptying out of the ducts 12 prior to disposal.

Similar connection is made in the FIG. 3 embodiment.

Referring to FIG. 3, a coaxial form of construction using thin walled copper tube conductors as in the device of FIG. 1, is shown. In this RF transmission line generally designated 25, an outer cover 20 which may be formed of rubber or vinyl or other abrasive resistant, insulating material is provided. The inner conductor comprises a plurality of copper tubes Zll similar to the copper tubes 12 of FIG. 2. The outer conductor consists of a plurality of similar copper tubes 22. The outer tubular conductors 22 are formed in an annular array concentric with .the inner annular array of tubular conductors 21 and radially spaced therefrom. These tubes extend along the length of the cable 25. In this embodiment as in the case of the device of PEG. 1, coolant flows through each of the tubes 21 of the inner concentric line (not numbered) and through each of the tubes 22 of the outer concentric line (not numbered). Connection is made by headers similar to those shown in FIG. 2 but adapted to fit the particular embodiment. For example, the headers could be in the shape of rings with the inner cable portion extending past the outer cable portion to enable two coolant inlets axially spaced and each perpendicular to its respective ring to be inserted. The radio frequency energy flows along the outer surfaces of the copper tube conductors and the coolant flows within them in the FIG. 3 embodiment also. The FIG.

3 embodiment is advantageous because it is equally flexible in all directions and because minimum radio frequency energy radiation losses are realized from coaxial transmission lines. Some loss of energy occurs at the lateral edges 27 and 28 of the device of FIGS. 1 and 2.

The thin-Walled copper tubes used in the invention (tubes 12 of FIG. 1 or tubes '21 and 22 of FIG. 3) may be annealed commercial copper having an outside diameter of /s-inch and a sidewall thickness of 0.0-1 5-inch.

While specific embodiments of the invention have been shown and described, it should be recognized that the invention is not limited thereto, since various modifications may be made Without departing from the spirit and scope of my invention. It is accordingly intended, in the appended claims, to cover all such variations as fall within the true spirit of the invention.

What is claimed is:

1. A flexible liquid-cooled radio frequency transmission line comprising a first and a second bank of relatively thin-Walled tubes of electrical energy conducting material, means to inject liquid coolant at the entrance at one end of each of said tubes for flow therethrough to the other tube end, means to inject radio frequency energy at one end of said tubes between said first and second banks, said radio frequency energy being propagated along the outer surfaces of each of said tubes, electrical in sulating means disposed in the interstices between and surrounding each of said banks of tubes and an outer abrasion resistant insulating covering disposed around said insulating means.

2. The apparatus of claim 1 wherein said transmission line is separated between banks of conducting tubes at each end and including a pair of header members one for each bank disposed at each of the ends of said transmission line, each of said banks of tubes being fixedly connected to its respective header, each of said headers having a hollow portion formed therein, means to insert coolant into said hollow portion, said hollow portion being disposed adjacent the ends of said tubes to provide entry of coolant into the interior of each of said tubes from its respective header.

3. A flexible radio frequency power transmission line comprising a silicone rubber compound, a plurality of relatively thin wall copper tubes embedded in said compound, a cover of electrically insulating material open at both ends to contain said tubes and compound, a header member having a hollow portion therein terminating said tubes at one end Within said header member hollow portion, said header being adapted to receive power input, and means to inject liquid coolant into said hollow portion for transmission along the interior of said tubes.

4. A radio frequency transmission line comprising a plurality of thin walled copper tubes arranged in at least two parallel rows for wave transmission therebetween, electrical insulating material disposed around and in the interstices between said tubes and said rows of tubes, a covering sheath to enclose said tubes and said insulating material, a header having a hollow portion terminating one end of each of said rows of tubes, means to introduce liquid coolant into each of said headers terminating at said one end of each of said rows of tubes and to permit egress of said liquid from the headers at the other end of each of said rows of tubes, said copper tubes being electrically connected to said headers.

5. A radio frequency transmission line comprising a first inner ring of copper tube members, a second concentric outer ring of copper tube members, electrical insulating material disposed in between and surrounding said tube members of said inner and outer rings, said inner and outer rings of tubes thereby forming a coaxial radio frequency transmission line providing a path for coolant to flow internally of each tube and radio frequency energy to flow along its surface with minimum loss of radiated energy.

6. A radio frequency transmission line comprising a first and a second group of copper tubes, said groups respectively corresponding to the first and second conductors of a two-conductor radio frequency transmission line electrical insulating material surrounding said tubes and means coupled to said tubes to elTect circulation oi coolant liquid along the inside of each of said tubes and to effect transmission of radio frequency power along the outer surfaces of each of said tubes.

1,539,490 Hunter May 26, 1925 6 Eby Nov. 3, Johnson Dec. 7, Meakin June 6, Dahlgren July 25,

FOREIGN PATENTS Great Britain July 11, Great Britain Apr. 11, 

1. A FLEXIBLE LIQUID-COOLED RADIO FREQUENCY TRANSMISSION LINE COMPRISING A FIRST AND SECOND BANK OF RELATIVELY THIN-WALLED TUBES OF ELECTRICAL ENERGY CONDUCTING MATERIAL, MEANS TO INJECT LIQUID COOLANT AT THE ENTRANCE AT ONE END OF EACH OF SAID TUBES FOR FLOW THERETHROUGH TO THE OTHER TUBE END, MEANS TO INJECT RADIO FREQUENCY ENERGY AT ONE END OF SAID TUBES BETWEEN SAID FIRST AND SECOND BANKS, SAID RADIO FREQUENCY ENERGY BEING PROPAGATED ALONG THE OUTER SURFACES OF EACH OF SAID TUBES, ELECTRICAL INSULATING MEANS DISPOSED IN THE INTERSTICES BETWEEN AND SURROUNDING EACH OF SAID BANKS OF TUBES AND AN OUTER ABRASION RESISTANT INSULATING COVERING DISPOSED AROUND SAID INSULTING MEANS. 